Compound Melting point in C Delta H fus (kJ/mol) Boiling Point in C Delta H vap

Question

Compound

Melting point in C

Delta H fus (kJ/mol)

Boiling Point in C

Delta H vap (kJ/mol)

HF

-83.11

4.577

19.54

25.18

HCl

-114.3

1.991

-84.9

17.53

HBr

-86.96

2.406

-67

19.27

HI

-50.91

2.871

-35.38

21.16

1.Calcluate the Delta S fus and Delta S vap for HF

2. Determine the entropy change when 7.3 mol of HF (g) condenses at atmopshereic pressure

Compound

Melting point in C

Delta H fus (kJ/mol)

Boiling Point in C

Delta H vap (kJ/mol)

HF

-83.11

4.577

19.54

25.18

HCl

-114.3

1.991

-84.9

17.53

HBr

-86.96

2.406

-67

19.27

HI

-50.91

2.871

-35.38

21.16

Explanation / Answer

Hi,

1) delta S = delta H / T

19.54C + 273.15 = 292.69 K
-83.1 C + 273.15 = 190.04 K

delta S vap = delta H vap / T = 25180J / 292.69 K = 86.03 J/K

delta S fus = delta H fus / T = 4577 J / 190.04 K = 24.08 J/K

2) ?S = n*Hfus/Tfus
?S = 7.3*4577/(190.04)
?S = 175.784 J/K = 0.1758 kJ/K

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